1. Field of the Invention
The present invention relates to a lithium ion secondary battery and preparation process of the same.
2. Description of the Related Art
Lithium ion secondary batteries have a light weight, a large capacity and high charge-discharge performance, and thus have been widely used in fields of mobile devices such as laptop computer and cellular phone and field of automobiles. Various studies have been done for establishing larger capacity and higher charge-discharge performance.
As such a lithium ion secondary battery, there has been known, for example as disclosed in FIG. 3 of JP2008-288214 A, a separator-type battery that a positive electrode composed of a positive electrode active material layer and a metal foil and a negative electrode composed of a negative electrode active material layer and a metal foil are integrated via a separator, and the separator is immersed with an electrolyte.
On the other hand, as disclosed in JP2011-70788 A, there has also been known a all-solid lithium ion secondary battery having a construction that a positive electrode, an electrolyte and a negative electrode are integrated without a separator.
Since the rate determining factor to enlarge the capacity and to enhance the charge-discharge performance of the lithium ion secondary battery is a rate of reaction of an electrolyte with a positive electrode active material and a negative electrode active material, it is important to make a distance between the positive electrode and the negative electrode shorter, and to increase areas of the positive and negative electrodes as large as possible. Considering this viewpoint, JP2011-70788 A proposes a process for preparing an all-solid battery which includes three-dimensional electrodes containing active materials of concavo-convex structure (convex linear active material parts having a high aspect ratio).
In order to enlarge the capacity and to enhance the charge-discharge performance, if the active material layer having concavo-convex structure as proposed in JP2011-70788 A is employed in the separator-type lithium ion secondary battery shown in JP2008-288214 A, for instance, there is a risk that the convex positive electrode active material part is entered into the corresponding concaved portion between the convex negative electrode active material parts, and destroys a separator. Of course when the separator is broken, there is a risk that battery performances are lost due to short-circuit of the positive electrode active material part and the negative electrode active material part.
Namely, it was difficult that the active material layer having concavo-convex structure in the all-solid lithium ion secondary battery as proposed in JP2011-70788 A was employed in the separator-type lithium ion secondary battery shown in JP2008-288214 A.
Considering the aforementioned problems, the object of the present invention is to provide a separator-type lithium ion secondary battery having large capacity and excellent charge-discharge performance without destroying the separator, even if an active material layer having concavo-convex structure of high aspect ratio.